Baseband signal converter for a wideband impulse radio receiver

ABSTRACT

A baseband signal converter device for an impulse radio receiver combines multiple converter circuits and an RF amplifier in a single integrated circuit package. Each converter circuit includes an integrator circuit that integrates a portion of each RF pulse during a sampling period triggered by a timing pulse generator. The integrator capacitor is isolated by a pair of Schottky diodes connected to a pair of load resistors. A current equalizer circuit equalizes the current flowing through the load resistors when the integrator is not sampling. Current steering logic transfers load current between the diodes and a constant bias circuit depending on whether a sampling pulse is present.

[0001] This application claims benefit of co-pending U.S. applicationSer. No. 09/356,384 filed Jul. 16, 1999, entitled “Baseband SignalConverter for a Wideband Impulse Radio Receiver”, the disclosure ofwhich is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to radio receiversadapted to receive and process wideband impulse radio signals. Moreparticularly, this invention pertains to devices and circuits foraccurately converting in an impulse radio receiver a series oftime-modulated radio pulses into a baseband signal.

[0003] There is a continuing need for the development of advancedwireless devices for communications of voice and data, for materialsmeasurement, navigation, environmental sensing, radar, security andnumerous other civilian and military applications of radio technology.Improvements are needed in the underlying technology to provide greaterreliability, greater accuracy, lower power consumption, lower cost,reduced size, and efficient use of the limited available spectrum.Conventional narrow band AM, FM, CDMA, TDMA and similar wirelesscommunications methods and systems have not fully met these needs.

[0004] However, there is an emerging technology called Impulse Radio(including Impulse Radar) (“IR”) that offers many potential advantagesin addressing these needs. Impulse radio was first fully described in aseries of patents including U.S. Pat. No. 4,641,317 (issued Feb. 3,1987), U.S. Pat. No. 4,813,057 (issued Mar. 14, 1989), U.S. Pat. No.4,979,186 (issued Dec. 18, 1990) and U.S. Pat. No. 5,303,108 (issuedNov. 8, 1994), all invented by Larry W. Fullerton and assigned to TimeDomain Corporation. The disclosure of each of these patents isincorporated in this patent specification by reference.

[0005] Impulse radio systems are generally characterized by theirtransmission of short duration broad band pulses on a relatively lowduty cycle. In some systems these pulses may approach a Gaussianmonocycle, where the instantaneous pulse bandwidth is on the order ofthe center frequency. The short pulse, low duty cycle mechanism producesa processing gain that may be utilized for interference rejection andchannelization. Because of the extremely wide instantaneous bandwidth ofthe pulse, the available processing gain far exceeds what is achievedusing typical conventional spread spectrum methods. This enables theutilization of many more channels at higher dynamic ranges and higherdata rates than are available in the typical conventional spreadspectrum system.

[0006] Impulse radio systems have further advantages in the resistanceto multipath effect. Because impulse radio signals are divided in timerather than in frequency, time related effects, such as multipathinterference, can be separated, resulting in lower average power andhigher reliability for a given power level.

[0007] Impulse radio techniques are also useful in radar systems.Impulse radar systems enjoy the combined advantages of very short pulsesat relatively low frequencies. The short pulses result in highresolution and the low frequency gives relatively high materialpenetration. If a radar system used a pulse of equivalent bandwidth at ahigher carrier frequency, the material penetration properties wouldusually be impaired. This combined advantage enables IR to be used forground penetrating radar for inspection of bridges, roads, runways,utilities and the like, and security applications, and to “see” throughwalls radar for emergency management situations.

[0008] Existing IR receivers typically use mixer or sampling technologywhich is large in size, inefficient in power consumption and which isdifficult to reproduce in a manufacturing environment. This results in ahigh cost to the user. Improvements are thus needed in convertertechnology to reduce size, weight, power consumption and cost and toimprove the manufacturing yield and reliability of these systems.

[0009] Impulse radio systems are not limited to transmitting andreceiving Gaussian monocycle pulses. However, some basic impulse radiotransmitters attempt to emit short Gaussian monocycle pulses having atightly controlled average pulse-to-pulse interval. A Gaussian monocycleis the first derivative of the Gaussian function. However, in a realworld environment, a perfect Gaussian pulse is not achievable. In thefrequency domain, this results in a slight reduction in the signalbandwidth. The signals transmitted by an IR transmitter, includingGaussian monocycles, signals having multiple cycles in a Gaussianenvelope, and their real world variations, are sometimes calledimpulses.

[0010] The Gaussian monocycle waveform is naturally a wide bandwidthsignal, with the center frequency and the bandwidth dependent on thewidth of the pulse. The bandwidth is approximately 160% of the centerfrequency. In practice, the center frequency of a monocycle pulse isapproximately the reciprocal of its length, and its bandwidth isapproximately equal to 1.6 times the center frequency. However, impulseradio systems can be implemented where the transmitted and/or receivedsignals have waveforms other than an ideal Gaussian monocycle.

[0011] Most prior art wireless communications systems use some variationof amplitude modulation (AM) or frequency modulation (FM) to communicatevoice or data with a radio carrier signal. However, impulse radiosystems can communicate information using a novel technique known aspulse position modulation. Pulse position modulation is a form of timemodulation in which the value of each instantaneous value or sample of amodulating signal (e.g., a voice or data signal) is caused to change ormodulate the position in time of a pulse. In the frequency domain, pulseposition modulation distributes the energy over more frequencies.

[0012] In some impulse radio communications, the time position(pulse-to-pulse interval) is preferably varied on a pulse-by-pulse basisby two separate components: an information component and a pseudo-randomcode component. Prior art spread spectrum radio systems make use ofpseudo-random codes to spread a narrow band information signal over arelatively wide band of frequencies. A spread spectrum receiver thencorrelates these signals to retrieve the original information signal.Unlike conventional spread spectrum systems, impulse radio systems donot need the pseudo-random code for energy spreading. In someapplications, impulse radio transmitters can use pulse widths of between20 and 0.1 nanoseconds (ns) and pulse-to-pulse intervals of between 2and 5000 ns. These narrow monocycle pulses have an inherently wideinformation bandwidth. (The information bandwidth, also referred tosimply as the “bandwidth”, is the range of frequencies in which one ormore characteristics of communications performance fall within specifiedlimits.)

[0013] Thus, in some impulse radio systems, the pseudo-random (PN) codecomponent is used for different purposes: channelization; energysmoothing in the frequency domain; and interference resistance.Channelization is a procedure employed to divide a communications pathinto a number of channels. In a system that does not use a codingcomponent, differentiating between separate transmitters would bedifficult. PN codes create channels, if there is low correlation and/orinterference among the codes being used. If there were a large number ofimpulse radio users within a confined area, there might be mutualinterference. Further, while the use of the PN coding minimizes thatinterference, as the number of users rises the probability of anindividual pulse from one user's sequence being received simultaneouslywith a pulse from another user's sequence increases. Fortunately,impulse radio systems can be designed so that they do not depend onreceiving every pulse. In such systems, the impulse radio receiver canperform a correlating, synchronous receiving function (at the RF level)that uses a statistical sampling of many pulses to recover thetransmitted information. Advanced impulse radio systems may utilizemultiple pulses to transmit each data bit of information, and each pulsemay be dithered in time to further smooth the spectrum to reduceinterference and improve channelization. These systems may also includea sub-carrier for improved interference resistance and implementationadvantages. In other embodiments of an impulse radio system, however,each “bit” of transmitted information can be represented by a singlepulse, with no coding component.

[0014] Energy smoothing in the frequency domain insures that impulseradio transmissions interfere minimally with conventional radio systems.In some impulse radio systems, optimal energy smoothing is obtained byapplying to each pulse a PN code component dither having a much largermagnitude than the information component dither.

[0015] Besides channelization and energy smoothing, the PN coding canalso makes impulse radio highly resistant to interference from all radiocommunications systems, including from other impulse radio transmitters.This is critical, as any other signals within the band occupied by animpulse signal can act as interference to the impulse radio. Becausethere are no unallocated bands at or above 1 GHz available for impulseradio systems, they must share spectrum with other conventional andimpulse radios without being adversely affected. Using a PN code canhelp impulse systems discriminate between the intended impulsetransmission and transmissions from others.

[0016] In many IR systems, the impulse radio receiver is a directconversion receiver with a single conversion stage that coherentlyconverts a series of pulses into a baseband signal. The baseband signalis the information channel for the basic impulse radio communicationssystem. In such systems, pulse trains, not single pulses, are used forcommunications. Accordingly, the impulse radio transmitter in suchsystems generates a train of pulses for each bit of information. Thedata rate of such an impulse radio transmission is only a fraction ofthe periodic timing signal used as a time base. Each data bit modulatesthe time position of many of the pulses of the periodic timing signal.This yields a modulated, coded timing signal that comprises a train ofidentical pulses for each single data bit. Some impulse radio receiverstypically integrate 200 or more pulses to yield the baseband output.Other systems use a “one pulse per bit” information transmission scheme.The number of pulses over which the receiver integrates is dependent ona number of variables, including pulse rate, bit rate, interferencelevels, and range.

[0017] A block diagram of one embodiment of a basic impulse radioreceiver 100 is shown in FIG. 7. The receiver 100 includes a receiveantenna 56 for receiving a propagated impulse radio signal 101. Thereceived signal is sent to a baseband signal converter 10 via a receivertransmission line 102, coupled to the receive antenna 56.

[0018] The receiver 100 also includes a decode timing modulator/decodesource 55 and an adjustable time base 57. The adjustable time base 57can be a voltage-controlled oscillator or, as shown, a variable delaygenerator 52 coupled to the output of a time base 51. The decode timingmodulator/decode source 55 generates a primary timing pulse (decodesignal 103) corresponding to the PN code used by the associated impulseradio transmitter (not shown) that transmitted the propagated signal101. The adjustable time base 57 generates a periodic timing signalhaving a train of template signal pulses with waveforms substantiallyequivalent to each pulse of the received signal 101.

[0019] The baseband signal conversion process performed by the converter10 includes a cross-correlation operation of the received signal 101with the decode signal 103. Integration over time of thecross-correlated received signal generates a baseband signal 104. Thebaseband signal 104 is then demodulated by a demodulator 50 to yield ademodulated information signal 105. The demodulated information signal105 is substantially identical to the information signal of thetransmitter that sent the received signal 101.

[0020] The baseband signal 104 is also coupled to a low pass filter 53.The low pass filter 53 generates an error signal 106 for an acquisitionand lock controller 54 to provide minor timing adjustments to theadjustable time base 57.

[0021] As noted above, the circuit or device in an impulse radioreceiver that converts the received impulses into a baseband signal issometimes referred to as a cross-correlator or sampler. The basebandsignal converter of an impulse radio receiver integrates one or morepulses to recover the baseband signal that contains the transmittedinformation. One embodiment of a cross-correlator device usable in animpulse radio receiver is described in U.S. Pat. No. 5,677,927, issuedOct. 14, 1997, and assigned to Time Domain Corporation. The disclosureof the '927 Patent is incorporated in this specification by reference.

[0022] Unfortunately, prior art baseband signal converter devices andcircuits have not been entirely satisfactory or are subject to inherentperformance limitations. In general, such converter devices have beenconstructed from discrete electronic components. The deficienciesinherent in discrete circuit designs include high power consumption,excessive device size, and a need for careful matching and/or “finetuning” of component values and/or operational parameters to produceaccurate and consistent performance. For example, the converter circuitdescribed in FIG. 2a of U.S. Pat. No. 4,979,186 uses a sampling bridgerequiring four diodes that must be carefully matched in performancecharacteristics. Similarly, the converter circuit design shown in FIG. 3of the '186 patent can produce a performance-degrading signal offsetthat varies over time and temperature. Moreover, the use of discreteelectronic components in the converter device places undesirable limitson the switching speeds of the active components used in the circuits,making it more difficult to perform the signal conversion process usingvery short sample times.

[0023] A further issue that has not been satisfactorily addressed byprior art baseband signal converter designs is flexibility inapplication. Some important impulse radio applications can be enabled orenhanced by concurrently operating multiple baseband converter circuitsin a single receiver. Scanning and rake receivers are examples ofimpulse radio applications where the use of two or more baseband signalconverters in a single receiver would be highly desirable.Unfortunately, a baseband signal converter device that integratesmultiple converter circuits in a single, low profile package has notbeen available in the prior art.

[0024] What is needed, then, is low profile, low power integratedcircuit device containing one or more circuits that can converttime-modulated radio pulses into a baseband signal, and that is capableof executing the conversion process accurately and consistently overtime and temperature using a short sample period.

SUMMARY OF THE INVENTION

[0025] In accordance with one object of the invention, a baseband signalconverter device combines three independent baseband converter circuitspackaged into a single integrated circuit. The device includes an RFinput coupled through a wideband variable gain amplifier tocorresponding RF signal inputs on each separate signal convertercircuit. Separate timing pulse inputs and baseband signal outputs areprovided external to the device, for each converter circuit. Thevariable gain amplifier has an auxiliary signal output coupled to apower detector to provide automatic gain control to the RF amplifier.

[0026] Each converter circuit in the device includes an integratorcircuit coupled to the RF signal input and a pulse generator coupled tothe timing pulse input. The pulse generator provides a sampling pulse tothe integrator to control the period during which the integratorintegrates each pulse in the RF input signal. The output of theintegrator is coupled through a buffer amplifier to a track and holdcircuit. A track and hold signal from a track and hold control circuitin the converter device circuit allows the track and hold circuit totrack and stabilize the output of the integrator. The output of thetrack and hold circuit provides a baseband signal output that is usableby a conventional impulse radio demodulator within an impulse radioreceiver.

[0027] The integrator circuit includes an integrator capacitor connectedto a resistive load through a pair of Schottky diodes. A current sourceand current steering logic steers the current between the load andintegrator capacitor and a separate constant bias circuit depending onwhether a sampling pulse is present. In addition, a current equalizercircuit monitors the voltage across the load resistor so that an averagezero voltage is maintained across the integrator capacitor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a block diagram of the baseband signal converter deviceof this invention, showing multiple converter circuits arranged forsingle or concurrent operation in a single integrated circuit.

[0029]FIG. 2 is a block diagram of one of the converter circuits as usedand shown in the device of FIG. 1.

[0030]FIG. 3 is a block diagram of the signal integrator circuit used inthe converter circuit of FIG. 2.

[0031]FIG. 4 is a schematic diagram of a first portion of a preferredembodiment of the signal integrator circuit of FIG. 3.

[0032]FIG. 5 is a schematic diagram of a second portion of the preferredembodiment of the signal integrator circuit of FIG. 3, showing thecurrent equalizer circuit.

[0033]FIG. 6 is a timing diagram showing the relationship between the RFpulses, timing signals, and baseband output signals as used andgenerated in the converter circuit of FIG. 2.

[0034]FIG. 7 is a block diagram of one embodiment of a wideband impulseradio receiver for converting time-modulated RF pulses into basebandsignals.

[0035]FIG. 8 is a plan view of the mechanical package and pinconnections for the integrated circuit device of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Baseband Converter Device Overview

[0037] A block diagram of one embodiment of the baseband converterdevice 10 of the present invention is shown in FIG. 1. Preferably, theconverter device 10 is manufactured as an application specificintegrated circuit (ASIC) in which the various device circuits arefabricated within a single integrated circuit device package 12. In theembodiment of FIG. 1, the device 10 includes three separate basebandconverter circuits 11. Each converter circuit 11 has an RF signal input15, a timing pulse input 14, and a baseband signal output 16. The RFsignal inputs 15 for each converter circuit 11 are internally connectedin parallel to the output 33 of a broadband, variable gain RF amplifier13. The input of amplifier 13 is connected to device RF input 17external to the device package 12 so that the device RF input 17 can beelectrically coupled to an antenna 56 as part of an impulse radioreceiver 100 (FIG. 7). Similarly, each timing pulse input 14 andbaseband signal output 16 defines a connection point external to devicepackage 12 so that the individual converter circuits 11 can becontrolled by separate timing signals to generate separate basebandsignals.

[0038] Preferably, the amplifier 13 will have an auxiliary output 34connected to the input of a power detector 18. The signal produced byamplifier 13 at auxiliary output 34 is a rectified, low frequencyauxiliary signal having electrical characteristics that correspond tovariations in the power level of the signals at RF input 17. The powerdetector 18 uses this auxiliary signal to generate a power level signalat an external terminal 19. The power level signal at terminal 19 can beused by an external signal processor (not shown) to determine if theamplifier 13 is overloaded and, if so, to calculate and generate a gainadjust signal at gain adjust input 7. This insures that device amplifier13 always operates to provide signals at RF signal inputs 15 that arewithin the operating range of converter circuits 11. In one embodimentof the device 10, the amplifier 13 will have a gain that is adjustablefrom 0 db to 30 db for wideband impulse radio signals between 1-4 GHz,having a magnitude of −10 dbm or lower. In addition, the amplifier 13should be non-dispersive to pulses with a noise figure of 15 dB or less.

[0039] Although the general techniques used to manufacture the device 10as an ASIC are well known in the art, the device circuits willpreferably be fabricated using a silicon germanium process. This willenhance the ability of the transistors and other switching componentswithin converter circuits 11 to process very short monocycle RF pulses,using timing pulses of 300 ps or less.

[0040] Converter Circuit Overview

[0041]FIG. 2 is a block diagram showing the internal sub-systems of apreferred embodiment of the converter circuit 11. The RF signal input 15is electrically connected to input 28 of an integrator circuit 23 toprovide a differential RF input signal V_(inp), V_(inn). The convertercircuit 11 also includes a track/hold control 20, a pulse generator 21,and a reset control 22, each having timing inputs connected in parallelto corresponding timing pulse input 14. This allows track/hold control20, pulse generator 21, and reset control 22 to function in response toa primary timing pulse (PG on FIG. 6) at timing pulse input 14.

[0042] In response to the primary timing pulse PG at input 14, the pulsegenerator 21 generates a sampling pulse as a differential signalV_(TRp), V_(TRn) at input 29 of integrator circuit 23. An external pulsewidth control input (FIG. 2) can be used to adjust the width of thesampling pulse to set the duration of the sampling and non-samplingperiods. Using the novel methods described below, the integrator circuit23 responds to the sampling pulse V_(TRp), V_(TRn) and integrates the RFinput signal V_(inp), V_(inn) to provide a differential integratoroutput signal V_(outp), V_(outn) at integrator output 27. The integratoroutput 27 is coupled to signal input 33 of track/hold circuit 26 througha buffer amplifier 25. The output of track/hold control 20 is connectedto control input 32 of track/hold circuit 26. Track/hold circuit 26, aswill be described below, generates a baseband output signal at basebandsignal output 16, in response to the integrator output signal V_(outp),V_(outn) and to a track and hold control signal at control input 32.

[0043] Integrator Circuit

[0044] Additional detail describing integrator circuit 23 is provided inblock diagram form in FIG. 3, and in the electrical schematics of FIGS.4 and 5. The differential RF input signal V_(inp), V_(inn) is providedto the bases of a differential transistor pair Q1, Q2 that forms, alongwith corresponding emitter resistors R3 and R4, the RF signal inputstage 47. The collectors of transistors Q1, Q2 are electricallyconnected to integrator capacitor C1 through a pair of Schottky diodesD1 and D2. A load 48, comprising load resistors R1 and R2, is connectedacross the integrator capacitor C1, again through diodes D1 and D2. Theload resistors R1 and R2 are also connected to a 5 VDC supply voltageVCC and to a current equalizer circuit 40 (FIG. 5) at a currentequalizer differential signal input (see signal C_(en), C_(ep) on FIGS.4 and 5).

[0045] A first current assist circuit 41, comprising differentialtransistor pair Q7, Q8, transistor Q14 and emitter resistor R9, isconnected across diode D1. Similarly, a second current assist circuit42, comprising differential transistor pair Q9, Q10, transistor Q12, andemitter resistor R11, is connected across diode D2. Transistors Q14 andQ12 (with emitter resistors R9 and R11) are driven by a constant basevoltage Vcs2 to act as current sources for current assist circuits 41,42 respectively. Current assist circuits 41 and 42 function to switchthe diodes D1 and D2 from a low impedance state to a high impedancestate, as described below.

[0046] The sampling pulse V_(TRp), V_(TRn) (provided at input 29 ofintegrator circuit 23) is coupled to the bases of differentialtransistor pair Q5, Q6 which form sampling pulse input circuit 46. Theemitters of transistors Q5 and Q6 are connected to the collector oftransistor Q11. Because the base of transistor Q11 is driven by aconstant bias voltage Vcs, Q11 forms, in conjunction with resistor RIO,a current source 43.

[0047] A constant bias circuit 45, comprising transistor pair Q3, Q4,and corresponding emitter resistors R5 and R6, is connected acrossintegrator capacitor C1, again through diodes D1 and D2, respectively.The bases of transistors Q3 and Q4 are connected to a common biasvoltage. In conjunction with current source 43 and sampling pulse inputcircuit 46, constant bias circuit 45 causes current to flow through theload 48 even when the sampling pulse V_(TRp) is low (non-samplingperiod), or when there is no RF pulse V_(inp), V_(inn) present. In otherwords, the load current sourced through Q11 is “steered” by this currentsteering logic during the absence of a positive sampling pulse (anon-sampling period when V_(TRp) is low at the base of Q5) through Q3and Q4. By steering the load current to Q3, Q4 (when V_(TRn) is low),and to D1, D2, Q8, and Q9 when V_(TRp) is high, rather than simplyswitching the load current on and off, the unwanted “ground bounce”noise that might otherwise be generated within the integrator circuit 23is minimized.

[0048] A pull up network 44, including transistor Q13 and resistors R7and R8, is connected between the supply voltage Vcc and the integratoroutput 27.

[0049] The novel current equalizer circuit 40 of this invention isschematically illustrated on FIG. 5. The fundamental purpose of currentequalizer circuit 40 is to adjust the current flow through loadresistors R1 and R2 when the converter circuit 11 is not sampling the RFinput signal V_(inp), V_(inn) that is when V_(TRp) is low. By adjustingthe current flow through the load resistors R1 and R2 during this time(no sampling pulse), a zero voltage is applied across diodes D1 and D2.This eliminates any offset voltage that would otherwise have to becorrected or compensated for.

[0050] The Schottky diodes D1 and D2 are in a high impedance state whenQ8 and Q9 are turned off. This isolates the integrator capacitor C1 fromthe rest of the integrator circuit 23. When the timing pulse PG (FIG. 2)at timing pulse input 14 is low, the reset control 22 causes the resetcircuit 24 (FIG. 2) to discharge the integrator capacitor C1. When thetiming pulse PG at timing pulse input 14 goes high, the reset control 22is disabled. Without the isolation provided by the diodes D1 and D2, thevoltage across capacitor C1 would decay too quickly and the ability ofthe integrator circuit 23 to process the narrow pulses inherent inimpulse radio would be degraded. As described with reference to thepreferred embodiment, the high impedance state achieved by the diodes D1and D2 must be such that the voltage across integrator capacitor C1 doesnot fall or “droop” by an amount that will create an error, before thetrack and hold circuit 26 can acquire it.

[0051] The current equalizer signal C_(en), C_(et) developed across theload resistors R1 and R2 is coupled to the bases of transistor pair Q19,Q20 of current equalizer circuit 40, through the low pass filter formedby R19, R20, and C2. The emitters of transistor Q19 and Q20 areconnected to the bases of transistor pair Q15 and Q16, respectively. Thecollectors of transistors Q15 and Q16 are connected to the supplyvoltage Vcc (through resistors R13, R14) and to the bases of transistorpair Q17, Q18. The collectors of transistors Q17 and Q18 are connecteddirectly across load resistors R1 and R2 (FIG. 4) respectively. Thebases of transistors Q25, Q26, Q27, and Q28 are driven by a constantbias voltage Vcs so that, in combination with emitter resistors R12,R21, R22, and R23, they act as current sources for transistors Q19, Q20,and for transistor pairs Q15, Q16 and Q17, Q18. Transistors Q21-Q24function as diodes to limit the collector voltage at Q25 and Q26 to alevel that is less than their breakdown voltages. Therefore, transistorsQ17 and Q18 can respond to changes in the current equalizer signalC_(en), C_(et) to adjust and equalize the current through load resistorsR1 and R2 (FIG. 4). This will maintain a zero average voltage across theintegrator capacitor C1 when the integrator circuit 23 is not samplingthe RF input signal V_(inp), V_(inn).

[0052] When the integrator is sampling during the sampling period(V_(TRp) is high), the current equalizer circuit 40 has little effectbecause transistors Q5, Q8 and Q9 are turned on for a short period thatis not significant compared to the time constant of the low pass filterformed by R19, R20, and C2 (FIG. 5). During this sampling period, thetransistor pairs Q7, Q8 and Q9, Q10 forward bias the diodes D1 and D2.This places the diodes D1 and D2 in a low impedance state such that thetime constant formed by the diodes in combination with capacitor C1 isless than the sampling period. When the integrator circuit 23 isfinished sampling (non-sampling period, V_(TRp) is low), Q8 and Q9 (aspart of current assist circuits 41 and 42) turn off as Q7 and Q10 turnon. This places the diodes D1 and D2 in a high impedance state, againisolating the integrator capacitor C1 from the rest of the integratorcircuit 23. The voltage across C1 (Voutp, Voutn) will then remainrelatively constant, corresponding to the RF input signal V_(inp),V_(inn-), integrated over the duration of the sampling pulse V_(TRp),V_(TRn). Using this novel arrangement, the integrator output signalVoutp, Voutn will not be critically affected by errors created bymismatched load resistors, ground bounce noise, or variations intemperature that may alter component values in the converter circuit 11.

[0053] Operation of the Baseband Converter Device

[0054] Referring now to FIGS. 1-7, the operation of the basebandconverter device 10 can be understood, with reference to a single RFmonocycle pulse V_(in) (FIG. 6). Assuming that the converter device 10is used in conjunction with a typical impulse radio receiver 100 asshown in FIG. 7, a periodic primary timing pulse PG is generated by adecode timing modulator/decode source 55 and coupled to timing pulseinput 14. Typically, each primary timing pulse PG will have a pulsewidth of 6 ns or less. The incoming primary timing pulse PG triggers thepulse generator 21 to generate a sampling pulse V_(TR) at input 29 ofintegrator circuit 23. As shown on FIG. 6, the sampling pulse V_(TR) isdelayed following the leading edge of primary timing pulse PG. Thelength of the delay is not critical and will typically be between 1 and2 ns. However, the length of the delay must be fixed precisely within afew picoseconds. The sampling pulse V_(TR) is narrow, having a fixedwidth that can range between 180 and 300 ps, such that an appropriatesegment of each RF input pulse V_(in) can be sampled and integrated. Asdescribed above, the length of the sampling pulse V_(TR) determines theperiod during which the integrator circuit 23 is processing andintegrating the RF pulses.

[0055] Looking at FIG. 4, the sampling pulse V_(TR) is provided asdifferential input signal V_(TRp), V_(TRn) at the bases of transistorpairs Q7, Q8; Q5, Q6; and Q9, Q10. Therefore, when the sampling pulseV_(TR) is high, Q8 is turned on, allowing a load current to flow throughR1, D1, Q8, and Q14. Similarly, during the sampling period defined bywhen sampling pulse V_(TR) is high, a load current will flow through R2,D2, Q9, and Q12. If there is an RF pulse (V_(inp) is high) during thetime that sampling pulse V_(TRp) is high, both transistors Q1 and Q5will be turned on. Because diodes D1 and D2 are in a low impedance stateat this time, a differential, non-zero voltage is applied acrossintegrator capacitor C1. At the end of the sampling period (V_(TRp) islow), transistor Q5 is turned off, and transistor Q6 is turned on,steering the load current through transistors Q3, Q4, Q6, and Q11, withdiodes D1 and D2 isolating capacitor C1. This produces an integratoroutput signal V_(outp), V_(outn) at integrator output 27 thatcorresponds to the sampled portion of the RF input pulse V_(in),integrated during the sampling period defined by the sampling pulseV_(TR).

[0056] As described above, during the period that the integrator circuit23 is not sampling (V_(TRp) is low), the current equalizer circuit 40 ismonitoring the voltages across load resistors R1 and R2. Any change involtage caused by unmatched resistors R1 and R2, or by variations inambient conditions, is compensated for by the current equalizer circuit40.

[0057] As best seen on FIG. 2, the integrator output signal V_(outp),V_(outn), after being amplified in buffer amplifier 25, is coupled toinput 33 of track and hold circuit 26. In response to a track and holdpulse (FIG. 6) generated by track and hold control circuit 20, andcoupled to input 32 of track and hold circuit 26, track and hold circuit26 “tracks” the integrator output V_(outp), V_(outn) of integratorcircuit 23 while the track and hold pulse is high and holds the trackedintegrator output during the period that the track and hold controlpulse is low. As shown in FIG. 6, the track and hold pulse, althoughtriggered by the primary timing pulse PG, is delayed to begin after theprimary timing pulse PG but before the sampling pulse V_(TR) begins. Thetrack and hold pulse must be wide enough to stabilize the voltage acrossC1, which is not changing when V_(TRp) is low. Preferably, the track andhold pulse will be 2-6 ns wide, +/−0.1 ns. The integrator outputV_(outp), V_(outn) signal, as tracked by the track and hold circuit 26,will then be held until the next RF pulse V_(in) appears, which willordinarily occur at approximate 100 ns intervals.

[0058] In the preferred embodiment, functional blocks 20 and 26 havebeen referred to and described using the phrase “track and hold.”However, those of skill in that art will recognize that a circuit orfunctional block referred to in the art as a “sample and hold” circuitwill function in an equivalent manner, in that all sample and holdcircuits have some finite “aperture” time during which the signal isbeing tracked.

[0059] In an impulse radio system where each data bit in the informationcomponent is represented by a single pulse, an impulse radio signal willcomprise a train of hundreds of time-modulated pulses (only one of whichis illustrated on FIG. 6). Therefore, the process described above willhave to be repeated many times within the converter device 10 in orderto obtain a complete baseband signal. To facilitate this, the resetcontrol circuit 22 generates a reset pulse on reset line 30 (FIG. 2)that goes low in response to the primary timing pulse PG. Essentially,except for unavoidable switching delays inherent in the circuitry, thereset pulse is an inverted version of the primary timing pulse PG. Thereset pulse is sent to a reset circuit 24 (a FET switch for example)that is coupled to output 27 of integrator circuit 23. When the resetpulse goes low, the integrator output 27 is effectively shorted by thereset device 24, so that the integration process can begin again with azero voltage across integration capacitor C1 (FIG. 3). The track andhold circuit 26 is conventional in design, and can simply be a FETswitch connected to a capacitor, where the FET switch is open during thehold period.

[0060] The output of the track and hold circuit 26 thereby provides, atbaseband output 16, a baseband output signal from the converter circuit11. The baseband output signal can then be coupled to the input of aconventional impulse radio demodulator 50 (FIG. 7) where the informationcomponent of the impulse radio signal can then be extracted.

[0061] The operation of the converter device 10 of this invention hasbeen described with only one converter circuit 11 being used by animpulse radio receiver, having the configuration represented by FIG. 7.However, the converter device 10 can be used in other receiverconfigurations (including radar systems) and for that purpose has beenprovided, as shown in FIG. 1, with three converter circuits 11 that canfunction independently. For example, an impulse radio scanning receiverwould benefit from using two converter circuits 11 concurrently to lookfor multiple transmissions having different PN code components (that is,signals transmitted on different “channels”). To improve the rejectionof unwanted multi-path signal interference, a rake receiver could usetwo or more converter circuits as well.

[0062] The application of the novel converter device of this inventionhas been described in one embodiment of a wideband impulse radio systemin which the impulse waveform (Vin) is shown on FIG. 2 as an idealizedGaussian monocycle. Due to system and component limitations, or forother design reasons, the actual waveform shown on FIG. 2 may be not bea true monocycle pulse. Persons of ordinary skill in the art willrecognize that impulse radio systems are not limited to any particularimpulse shape or characteristic. The converter device of this inventioncan be used in impulse radio systems where the RF impulses beingconverted are not monocycles and/or do not have a Gaussian wave shape,where the impulses are transmitted at different frequencies andbandwidths, and with or without coding components being applied to thesignal.

[0063] Thus, although there have been described particular embodimentsof the present invention of a new and useful Baseband Signal Converterfor a Wideband Impulse Radio Receiver, it is not intended that suchreferences be construed as limitations upon the scope of this inventionexcept as set forth in the following claims. Also, although certainembodiments of the invention have been described in combination withspecified functional and operational parameters, these parameters areprovided for illustrative purposes only and are not deemed limitationson the scope of the invention.

What is claimed is:
 1. A device for converting RF pulses received by awideband impulse radio receiver into one or more baseband signals, thedevice comprising: a. an RF input for receiving the RF pulses; b.multiple timing inputs for receiving separate timing signals; c.multiple converter circuits, the converter circuits each having a signalinput electrically coupled in parallel to the RF input; d. eachconverter circuit having a second input electrically coupled to one ofthe timing inputs such that each converter circuit can receive one ofthe separate timing signals; e. each converter circuit having a basebandsignal output; and f. the device is packaged as a single integratedcircuit in which the converter circuits are arranged on a commonsubstrate for single or concurrent operation.
 2. The device of claim 1further comprising an RF amplifier having an input coupled to the RFinput and an output coupled to the signal inputs of the convertercircuits.
 3. The device of claim 2 further comprising a power detectorcircuit operatively connected to the RF amplifier, the power detectorcircuit responsive to the RF amplifier.
 4. The device of claim 1 whereineach converter circuit includes a signal integrator that is responsiveto one of the separate timing signals and that integrates the RF pulsesto provide a converter output signal coupled to a corresponding one ofthe baseband signal outputs.
 5. A wideband impulse radio receivercomprising: a. an antenna input for receiving time-modulated RF pulses;b. multiple converter circuits, each converter circuit having an RFsignal input electrically connected in parallel with the RF signalinputs on the other converter circuits and to the antenna input, atiming input electrically connected to a corresponding timing signalgenerator, and a baseband signal output; c. each converter circuitoperable to convert at least a portion of the RF pulses into a basebandsignal at a corresponding one of the baseband signal outputs; and d. theconverter circuits and timing signal generators are arranged on a commonsubstrate within a single integrated circuit package such that one ormore of the converter circuits can function separately or concurrentlyto produce separate baseband signals at the corresponding basebandsignal outputs.
 6. The impulse radio receiver of claim 5 furthercomprising a demodulator operatively connected to each of the basebandoutputs.
 7. The impulse radio receiver of claim 6 wherein the RF pulsesare modulated by a coding component and the receiver further comprises adecode timer operatively connected to each of the converter circuits.